INTERFERENCE EFFECTS IN WHITE CLOVER GENOTYPES GROWN AS PURE STANDS AND BINARY-MIXTURES WITH DIFFERENT GRASS SPECIES AND VARIETIES

Six white clover genotypes and eight grass varieties belonging to four different species were grown both in monoculture and as grass-legume binary mixtures in dense swards for two years under a mowing regime an d a management including N fertilization. Dry matter yield and yield-r elated traits were recorded to investigate some aspects of inter-speci fic interference in white clover-based mixtures and to define a method ology for selecting genotypes of this clover suited to conditions of a ssociation. Clover was at a competitive disadvantage in most mixtures. Differences among grasses for aggressiveness were related more to var iety vigour than to species. Clover compatibility proved specific only in relation to grass vigour. Variation among clovers for tolerance to competitive stress involved significant cross-over interactions passi ng from monoculture to severe stress conditions for clover yield and o ther traits, and was related positively to stolen density and negative ly to yield and leaf gigantism traits recorded in monoculture. Clover selection for high levels of competitive stress seems possible either by genotype assessment in stress conditions or by a combination of hig h yield and stolen density assessed in monoculture.